Water-soluble films are well known in the art. Water-soluble films have many applications, including non-edible forms, such as packaging, and edible forms, wherein the film itself is or contains an edible article. Edible films are known for uses such as delivery of therapeutic agents, breath freshening agents, food ingredients including but not limited to baking ingredients such as dough modifiers and flavors. The films can be formed into water-soluble packets for storing or delivering various compositions, edible or non-edible.
Common methods for sealing water-soluble films formed into packets or pouches include heat sealing and solution sealing. With heat sealing, pouches may be formed by placing two sheets of water-soluble film together, heat-sealing three edges, filling with a suitable composition, and then heat sealing the forth edge to form a sealed pouch. In a solution sealing process, solvent is applied to the film material to form a seal between the solvated film and another film. Water is a common solvent for solution sealing of water-soluble pouches because it is low cost, non-toxic, and readily available such that, when applied at appropriate levels, it can result in strong seals which prevent solid/liquid leakage from the resulting pouch.
While solution sealing can have advantages over heat sealing, solution sealing has been found unsuitable for many water-soluble films. Some water-soluble films may form solution seals with insufficient strength to maintain structural integrity during their useful lives. In other cases, the water-soluble film may be relatively susceptible to rapid dissolution by the sealing solution, thus destroying the film and/or preventing seal formation with sufficient strength. For example, on rapidly dissolving water-soluble films such as polyvinyl alcohol, water can be too aggressive in dissolving the film, resulting in film burn-through and preventing quality seal formation. For some water-soluble films, in particular for thin films such as 1.5 mil-thick films, there is no known method or corresponding sealing solution for effectively sealing the films.